Exemplary embodiments of the invention relate to a fuel cell system having at least one fuel cell and a humidifying device.
Fuel cell systems are known from the general prior art. They may be designed on the as a proton exchange membrane (PEM) fuel cell, for example, and may generate electrical power from hydrogen or a hydrogen-containing gas and atmospheric oxygen. This electrical power may then be used for various purposes. One preferred use of fuel cell systems of this type is in vehicles for generating electrical drive power.
Such fuel cell systems typically have humidifiers by means of which in general a supply air flow to a cathode chamber of the fuel cell is humidified to keep the comparatively sensitive membranes of the PEM fuel cell from drying out and to ensure their long-term functionality. Such a humidifier is discussed in German patent document DE 101 10 419 A1, for example. In addition to the humidifier itself, the system has a water separator by means of which water may be collected and injected as auxiliary humidification into the supply air flow.
A particular design concerning the specific arrangement of the humidifier and the water separator with respect to one another is also described in German patent document DE 10 2008 005 649 A1.
Furthermore, DE 10 2007 003 144 A1 discloses a design in which there is functional integration of humidification and cooling in a single component.
Operation of a fuel cell system always results in product water, which must be discharged from the system to ensure the gas supply and thus the functionality of the fuel cell. This water may be additionally used for humidifying the supply air by means of the above-described humidifier. In particular for so-called freezing starts, i.e., starting the fuel cell system at temperatures below the freezing point, and during warm-up of the fuel cell system that is associated with considerable equipment outlay, possible blockages from liquid water, in particular in frozen form, must be avoided. The design typically includes electrical heating of, for example, drainage lines downstream from water separators and/or valves situated in these lines. In addition to the significant energy expenditure, the design as well as the control necessary for this purpose entail additional costs and increase the complexity and therefore the susceptibility to malfunction of the fuel cell system. This is a major drawback, in particular for fuel cell systems which are to be used in vehicles for providing electrical drive power. However, since these systems are frequently switched off under temperature conditions in which freezing of the system is possible before restarting, this equipment design has thus far been unavoidable.
Exemplary embodiments of the present invention avoid or greatly simplify this equipment design, and thus provide a cost-effective and energy-efficient fuel cell system.
In the fuel cell system according to the invention, the humidifying device has an integrated anode water separator, through which exhaust gas from the anode chamber of the fuel cell flows, for humidifying the supply air flow with the moisture contained in the exhaust air flow. This integration of the anode water separator into the humidifying device, through which volume flows from the cathode side otherwise pass, allows advantages with regard to installation space and weight. In addition, in the fuel cell system according to the invention a simple integrated design is made possible in which water separated in the anode water separator may be easily discharged into one of the gas flows from or to the cathode chamber of the fuel cell, since these gas flows likewise pass through the integrated humidifying device. Additional lines for such water that would have to be appropriately heated and/or insulated may be dispensed with.
In another particularly favorable and advantageous embodiment of the fuel cell system according to the invention, a cathode water separator for the exhaust air flow is integrated into the humidifying device. Such a cathode water separator may be particularly advantageous when the exhaust air flow downstream from the humidifying device passes into a turbine or a expander, for example, where typically no droplets are supposed to arrive, since they could easily damage a turbine running at extremely high speed, for example. In addition, in the event of freezing, while the system is switched off this could result in blockage of the expander or the turbine, thus greatly slowing down the restarting process. Thus, according to this meaningful and advantageous embodiment, in addition to the anode water separator the cathode water separator may also have a design that is integrated into the humidifying device. Here as well, complicated lines to be heated electrically and/or insulated, for example, for water discharge may be dispensed with. Furthermore, it is possible to connect the anode water separator to the cathode water separator, so that, for example, the water may be discharged from the fuel cell system via a single shared exhaust line.
In another advantageous embodiment of the fuel cell system according to the invention at least one heat exchanger, through which a cooling medium of a cooling circuit of the fuel cell flows, has a design that is integrated into the humidifying device. Such a heat exchanger, or for example also two heat exchangers through which flow passes in parallel, which is/are associated with the actual humidifier and the water separator(s) according to the above-described embodiment, allow(s) rapid heating and rapid thawing of the humidifying device as needed, for example during a freezing start. The anode water separator and optionally the cathode water separator as well as the actual humidifier may thus be rapidly thawed and brought to operating temperature. Electric heaters may thus be dispensed with. Via the connection to the cooling circuit, it is also possible to delay the cooling of the humidifying device, so that the humidifying device is able to discharge separated water to the surroundings of the fuel cell system for a very long period of time.
In another favorable and advantageous variant of the fuel cell system according to the invention, the anode water separator is switchably connected to one or more components of the cathode side via at least one valve unit. Such a valve unit between the anode water separator and a component of the cathode side, for example a cathode water separator, provided that it is present, represents a very simple and efficient way to discharge water and optionally gas within the humidifying device from an anode recirculation into the region of the supply air flow or the exhaust air flow on the cathode side. The design is highly integrated and very compact, and may dispense with lines which would have to be insulated and possibly heated.
In one very advantageous refinement, the anode water separator is switchably connected to one or more components of the cathode side via at least two valve units, one of the valve units branching off in the anode water separator in such a way that primarily a liquid volume flow passes through this valve unit, and the other of the valve units branching off in the anode water separator in such a way that primarily a gaseous volume flow passes through this valve unit. As the result of such a design having two valve units in different areas of the anode water separator, the discharge of liquid and gas (which typically contains residual hydrogen and inert gases), which may have accumulated in an anode circuit may be subdivided in the humidifying device. Thus, the water may be metered to a component on the cathode side that is different from that for the gas. For example, the water may pass into an exhaust air flow or a cathode water separator, while the gas, for example, passes into a supply air flow to the fuel cell in order to render harmless any residual hydrogen at the catalysts of the cathode chamber.
In another very favorable and advantageous embodiment of the fuel cell system according to the invention, the fuel cell and the humidifying device have a design that is integrated to form a structural unit, so that when the valve unit is open, water from the anode water separator is able to flow into the cathode chamber of the fuel cell due to the force of gravity. Such a design may introduce water and gas into the cathode chamber of the fuel cell without the need for lines, since in this advantageous refinement of the fuel cell system the humidifying device and the fuel cell are integrated with one another. The humidifying device is situated above the fuel cell in the direction of the force of gravity in such a way that a valve unit for emptying the anode water separator introduces at least the water and possibly the gas into the region of the cathode chamber of the fuel cell. Here as well, heating or insulation is not necessary, since line elements which connect the components to one another may be largely dispensed with.